1. Field of the Invention
This invention relates to a method for deaerating a liquid in a substantially closed liquid circulation system, in which an amount of liquid is withdrawn from the circulation system and is introduced via a valve into a closed reservoir, by means of a pump the pressure in the reservoir is reduced for deaerating the liquid and the liquid is sucked from the reservoir and added to the circulation system again, and separated air is discharged via a vent unit to the environment. This invention also relates to an apparatus for practicing such method.
2. Background Art
A method of the type described in the opening paragraph hereof is known from European patent application A3-0 187 683, more specifically FIG. 5 of that publication and the discussion thereof. In this known method, liquid is added to the reservoir until a level gauge gives a first signal, which causes the valve to close and the pump, having been stationary up to that moment, to start operating. The pumping action creates an underpressure in the reservoir, so that water is sucked in via a pipe which branches off from the supply at a point upstream of the valve and which includes a reducing valve. As the water flows into the reservoir, it is degassed due to the reduced pressure condition prevailing there. Due to the action of the pump, the liquid level in the reservoir falls until the level gauge gives a second signal, which switches off the pump and opens the valve. The water to be deaerated now flowing in displaces the separated air already present in the reservoir via a float valve and a non-return valve into the environment. As soon as sufficient water has flowed through the valve into the reservoir, the level gauge gives a first signal again, thereby initiating a next air separation phase. Thus the process comprises an air separation phase, in which the pump rotates and the valve is closed, and an air blow-off phase, in which the pump is stationary and the valve is open. In other words, the process is a discontinuous process in which various valves have to be controlled and the pump has to be set in operation and stopped. This disadvantage is recognized and an attempt is made to reduce the less desired effect thereof by designing the level gauge in such a manner that the air separation phase lasts as long as possible.